Amino Acids and Proteins

Question 1

Amino acids contain what two functional groups.

Answer 1

• amine NH2• carboxyl COOH

Question 2

What is an a amino acid?

Answer 2

There are four different groups attached to the central (chiral) carbon.Chiral molecules have two optical isomers called enantiomers.

Question 3

What is a zwitterion?

Answer 3

A dipolar ion- it has both a positive and negative charge in different parts of the molecule.Only exist near an amino acid’s isoelectric point.

Question 4

What is the isoelectric point?

Answer 4

This is the pH where the average overall charge on the amino acid is zero.

Question 5

How are peptides formed?

Answer 5

α-amino acids can join up together to form peptides via an amide or peptide link• 2 amino acids joined dipeptide• 3 amino acids joined tripeptide• many amino acids joined polypeptide

Question 6

Peptides can be broken down into their constituent amino acids by…

Answer 6

Hydrolysis• attack takes place at the slightly positive C of the C=O• the C-N bond next to the C=O is broken• hydrolysis with just water is not feasible• hydrolysis in alkaline/acid conditions is quicker• hydrolysis in acid/alkaline conditions (e.g. NaOH) will produce salts

Question 7

What are proteins?

Answer 7

• polypeptides with high molecular masses• chains can be lined up with each other• the C=O and N-H bonds are polar due to a difference in electronegativity• hydrogen bonding exists between chainsun

Question 8

State the general formula of an a amino acid.

Answer 8

RCH(NH2)COOH

Question 9

What is thin layer chromatography?

Answer 9

This separates components by adsorption.A solvent spreads up the plate as it is dipped into a solvent.The different substances move up with it but at different rates- so they separate out.

Question 10

How do you work out what was in the mixture in thin layer chromatography?

Answer 10

Calculating Rf value = distance travelled by spot/ distance travelled by solvent, you can then look them up in a table of known values.

Question 11

What’s a racemic mixture?

Answer 11

A solution in which both enantiomers of a compound are present in equal amounts is called a racemic mixture, or racemate. Problem is only one enantiomer may be help and the other may be harmful.

Question 12

If the conditions are more acidic than the isoelectric point…

Answer 12

The -NH2 group is likely to be protonated.

Question 13

If the conditions are more basic than the isoelectric point…

Answer 13

The -COOH group is likely to lose its proton.

Question 14

What is meant the term stereoisomer?

Answer 14

Molecules with the same structure but different arrangements in space.

Question 15

How does cis-trans isomerism arise?

Answer 15

The double bond does not rotate.

Question 16

What structural feature causes optical isomerism in organic molecules?

Answer 16

Molecules with optical isomers…- are chiral- have four different groups attached to the carbon- the mirror images cannot be superimposed

Question 17

What’s a chiral carbon?

Answer 17

Carbon which has four different groups attached to it. It’s possible to arrange the groups in different ways to create enantiomers or optical isomers.

Question 18

What are the methods for producing single enantiomer drugs?

Answer 18

Using natural enzymes or bacteriaUsing naturally occurring single optical isomer compoundsUsing chemical chiral synthesisUsing chiral synthesis